How to handle DMARC failures when email is forwarded by recipients?
Michael Ko
Co-founder & CEO, Suped
Published 4 May 2025
Updated 19 Aug 2025
6 min read
Email forwarding is a common practice for many users, allowing them to consolidate mailboxes or redirect specific types of messages. However, for email senders, this seemingly innocuous act can lead to significant DMARC failures, impacting deliverability and trust. This is particularly problematic for critical alerts or important notifications where timely and reliable delivery is paramount.
The challenge intensifies when a sender has limited control over the recipient's mail infrastructure, such as when corporate recipients forward emails through systems like Microsoft 365 or various cloud security solutions. These intermediaries often alter email headers or the sending path, inadvertently breaking the authentication chains that DMARC relies upon.
Understanding why these failures occur and what steps can be taken from the sender's side to mitigate them is crucial for maintaining a strong email reputation and ensuring your messages reach their intended destination.
When an email is forwarded, especially via automated rules or mail systems, the original SPF and DKIM authentication can break. SPF (Sender Policy Framework) checks the sending IP address against a list of authorized IPs in the sender's DNS record. When an email is forwarded, it typically passes through a new server, changing the sending IP. This new IP is often not authorized in the original sender's SPF record, causing SPF to fail.
Similarly, DKIM (DomainKeys Identified Mail) uses a digital signature to verify that the email content and certain headers have not been altered in transit. Forwarding servers may modify headers, add footers, or even re-encode the message body. Even minor changes invalidate the original DKIM signature, leading to a DKIM failure. You can learn more about how email forwarding can break DMARC from this external resource.
DMARC (Domain-based Message Authentication, Reporting, and Conformance) relies on both SPF and DKIM passing and aligning with the 'From' domain. If either SPF or DKIM (or both) fail due to forwarding, the DMARC check will also fail. This is why you might see DMARC reports indicating authentication failures even for legitimate emails that were originally properly authenticated. I often encounter clients who wonder why DMARC authentication fails when SPF and DKIM pass.
The impact of DMARC failure on forwarded emails can be severe, especially if the sending domain has a strong DMARC policy set to 'quarantine' or 'reject'. In such cases, the forwarded email might be moved to spam or not delivered at all. This poses a significant problem for critical alerts or transactional emails, where non-delivery can have real-world consequences.
Strategies for senders
When you're the sender and don't control the recipient's forwarding setup, your options for directly fixing the DMARC failures are limited. However, you can implement strategies to minimize the negative impact.
One key approach is to carefully manage your DMARC policy. While a 'reject' policy is ideal for preventing spoofing, it can be problematic for forwarded legitimate emails. Many organizations choose a 'quarantine' policy (p=quarantine) to allow recipient servers to place non-compliant messages in spam rather than blocking them outright. This provides a balance between security and deliverability for forwarded mail.
Communicating with your recipients is another vital step. While it may not be feasible to reach every individual, providing clear guidance on how to allow-list your domain or configure their forwarding rules correctly can make a significant difference. Educating recipients about the importance of email authentication helps them understand why your messages might be blocked, enabling them to take action on their end.
Leveraging DMARC reports and ARC
DMARC reports (RUA and RUF) are invaluable for identifying forwarding issues. RUA reports provide aggregated data on DMARC authentication results, including information on how many messages failed and from which IP addresses. By analyzing these reports, you can identify specific recipient domains or IP ranges where forwarding is consistently causing DMARC failures. This data helps prioritize outreach to problem recipients or adjust your sending strategy.
For instance, if you notice a high volume of DMARC failures from Microsoft 365 IP ranges, it strongly suggests forwarding issues within those organizations. While you can't directly intervene, this insight helps inform your communication strategy with those specific clients.
Another powerful mechanism is ARC (Authenticated Received Chain). ARC is a protocol that allows forwarding servers to preserve email authentication results across multiple hops. When an email is forwarded, the forwarding server adds an ARC seal, which includes the original authentication results (SPF, DKIM, DMARC) and a signature from the forwarding server itself. This allows the final recipient mail server to verify the authenticity of the forwarding chain, even if SPF or DKIM break during the process.
While you, as the original sender, cannot force recipient mail servers to implement ARC, you can encourage its adoption by highlighting its benefits. For example, Google recommends adding ARC headers to reduce the likelihood of forwarded messages being rejected or marked as spam. For more detailed information, the IETF draft on mailing lists and mail forwarders versus DMARC provides technical insights.
Understanding and troubleshooting DMARC failures involves a combination of technical analysis and proactive communication. While you can't control every aspect of a recipient's mail flow, equipping yourself with knowledge and employing best practices can significantly improve your email deliverability even in complex forwarding scenarios.
Final thoughts on DMARC and forwarding
Dealing with DMARC failures caused by email forwarding can be a persistent challenge, especially when dealing with critical alerts or transactional emails. While direct control over recipient forwarding setups is often impossible, understanding the underlying mechanisms and implementing strategic sender-side adjustments can significantly mitigate the impact.
Focusing on strong DKIM implementation, carefully managing your DMARC policy, and actively analyzing DMARC reports are key steps. Additionally, advocating for and supporting the adoption of ARC by recipient systems will progressively improve the landscape for forwarded email authentication. It's a continuous effort to ensure your legitimate emails bypass the spam folder and reach their intended recipients, regardless of their forwarding configurations.
Views from the trenches
Best practices
Ensure your initial SPF and DKIM records are perfectly configured and aligned for your sending domain, as this is the foundation for DMARC success, even if forwarding breaks them later.
Analyze DMARC reports regularly to identify specific domains or IP addresses that frequently cause failures due to forwarding, allowing for targeted communication if possible.
Consider educating your key recipients about the impact of email forwarding on DMARC and how they can configure their systems to properly handle authenticated email.
Common pitfalls
Setting a DMARC 'p=reject' policy prematurely without fully understanding the volume of legitimate forwarded emails, leading to unintended delivery failures.
Ignoring DMARC reports, thus missing crucial insights into where and why your emails are failing authentication checks when forwarded.
Assuming that all forwarding mechanisms behave the same way, when in reality, different systems (e.g., Microsoft 365, internal appliances) handle headers and authentication differently.
Expert tips
If direct outreach to recipients isn't feasible, explore alternative notification channels for critical alerts, such as SMS, webhooks, or in-app notifications, to ensure delivery.
For subdomains used for automated alerts, consider a less restrictive DMARC policy (e.g., p=quarantine) than your primary domain, especially if you anticipate high forwarding rates.
Investigate the specific forwarding practices of major mailbox providers and common corporate systems to anticipate authentication challenges and proactively address them.
Marketer view
Marketer from Email Geeks says they have seen many DMARC failures with Microsoft 365 accounts where organizations do not set up forwarding rules correctly, and suggested targeted outreach to recipients to allow-list the sender if mail flow cannot be changed.
2024-04-02 - Email Geeks
Marketer view
Marketer from Email Geeks says they found it difficult to pinpoint the source of DMARC failures when they only knew they were coming from Google Workspace. It turned out to be internal tech team alerts within their own Google Workspace account.
Microsoft 365 IP ranges, it strongly suggests forwarding issues within those organizations. While you can't directly intervene, this insight helps inform your communication strategy with those specific clients.
